Method of manufacturing rayon fiber



Sept. 15, 1970 R. T. cARNEY ETAL 3,529,052

METHOD -OF MANUFACTURING RAYON FIBER Filed Aug. 29, 19s? United States Patent O 3,529,052 METHOD F MANUFACTURING RAYON FIBER Rufus T. Carney, Wayne, and Charles J. Geyer, Jr.,

Berwyn, Pa., assignors to EMC Corporation, Philadelphia, Pa., a corporation of Delaware Continuation-impart of application Ser. No. 261,086, Feb. 26, 1963. This application Aug. 29, 1967, Ser. No. 667,038

Int. Cl. Dolf 3/28 U.S. Cl. 264-195 4 Claims ABSTRACT 0F THE DlSCLOSURE Viscose rayon fibers formed from viscose including certain amino viscose additives contain zinc dithiocarbamate compounds which seriously interfere with carding. Cardability is improved by-subjecting the staple bers in a relaxed state to a treatment with a dilute acid solution to dissolve and remove the carbamate compound.

This application is a continuation-impart of our copending application Ser. No. 261,086, filed Feb. 26, 1963 and now abandoned, entitled Rayon Fiber and Method of Manufacture.

This invention relates to high wet modulus regenerated cellulose fibers. More particularly, this invention relates to high wet modulus regenerated ecllulose staple fiber of improved cardability, and processes for its manufacture.

High wet modulus fibers of the prior art were found to have certain shortcomings that limited their use. Many were brittle and were subject to fibrillation, and it was also found that they had poor cardability. An excessive amount of the fiber loaded the card and was, in etlect,

lost to the textile operation.

This invention has for its principal object to provide high wet modulus regenerated cellulose fibers of improved cardability.

Another object of this invention is to provide high Wet modulus regenerated cellulose fibers that are at least relatively non-fbrillatable and that have improved cardability.

An additional object of the invention is to provide processes for the manufacture of high Wet modulus regenerated cellulose fibers of improved cardability.

A further object of the invention is to provide processes for the manufacture of high wet modulus regenerated cellulose fibers that are at least relatively nonfibrillatable and that have improved cardability.

Other objects and advantages of the invention will be apparent from the following description and accompanying drawing.

In the drawing:

FIG. l is a diagrammatic view of a form of apparatus for practicing the process and manufacturing high Wet modulus regenerated cellulose fiber of the present invention.

The regenerated cellulose fiber of the present invention has a high Wet modulus of at least and generally in the range of 10 to 20. The fiber is non-fibrillatable or relatively non-fibrillatable with a water flow number of no more than 25. The fibers are characterized by having a low card load factor, namely, a card load factor less than 3.25. The fibers of this invention may be of a wide range of deniers and staple fiber lengths, for example, from 1 to 3 denier and from 11/2 to 2 inch staple length.

A particularly unique characteristic of the present fiber is that it resembles cotton very closely in its wet modulus, shrinkage characteristics and ultimate extensibility or elongation in both the wet and conditioned states. Be-

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cause of these characteristics, the fiber may replace cotton for many textile purposes or may be blended with cotton. It also possesses the desirable characteristics of other viscose rayon textile bers with respect to luster, softness and hand. Fabrics formed of the fiber may be stabilized by physically compressing the fabric in a warpwise .direction by well known methods such as the process associated with the trademark Sanforize as disclosed in the U.S. patent to Cluett 1,861,422, May 31, 1932.

One of the factors which has greatly limited the blending of textile grades of rayon iibers with cotton has been the appreciable loss, about 30%, in strength of rayon fibers when subjected to the usual caustic soda treatment used in mercerizing cotton yarns and fabrics. Because of this appreciable loss in strength and the diiculties encountered in attempting to impart dimensional stability to rayon fibers and fabrics, the rayon content of blends of cotton and the prior art rayon fibers has been restricted to a maximum of about 30%. The fiber of this invention, on the other hand, when subjected to a mercerization treatment results in a loss of tensile strength of only 10% to 14%. Furthermore, the ability to stabilize dimensionally the fabrics formed of this fiber by physical treatment of the fabric permits the use of blends of cotton and this new fiber wherein the rayon content may be from 10% or less to about 70% to 75%.

The wet modulus, as used herein, is au average wet modulus and is the amount of stress in grams per denier of the fiber required to stretch the fully wet fiber 5% of its length divided by 0.05 which is the strain. The extensibility or elongation is the amount of stretching generally reported in percentage of the fiber length at the point of breaking of the fiber. Measurements of Wet modulus and elongation or extensibility may be made on the conventional Instron Tensile Tester by conventional procedure. The Wet modulus of the viscose rayon fiber of the present invention varies between about 10 and 20. This characteristic is just slightly less than the corresponding characteristic of cotton fibers and, hence, the fiber stretches to about the same extent as cotton during weaving and finishing of a woven fabric. This characteristic also contributes to the ability of increasing the rayon content of blends of cotton and rayon to 70% to This factor is a measure of the resistance of the fiber to stretching or elongation when subjected to tension. The elongation or extensibility of the fiber is generally within the range of from 8 to 22% when wet and about 9 to 15% in the conditioned state.

Woven fabrics formed entirely of these viscose rayon fibers have a residual shrinkage or will shrink after successive washings about 5% or less which is again about the same as untreated cotton fabrics. The residual shrinkage of a woven fabric can be reduced to about 2.2% by subjecting the fabric to a compression treatment in the direction of the warp as shown in the U.S. patent to Cluett 1,861,422. This degree of shrinkage is similar to the residual shrinkage for corresponding cotton fabrics. Fabrics formed of the fiber exhibit about the same wet Warp tensile strength as those formed of coton. However, they exhibit a warp tensile strength in a conditioned state of about 25% greater than corresponding cotton fabrics.

Prior rayon fibers having a high strength and a high wet modulus have been characterized in having an undesirable property of fibrillating excessively. A very distinctive attribute of the fibers of this invention is their low fibrillation which is about the same as that of conventional textile grade rayon.

Fibrillaion is the splitting or peeling off of portions of the fiber. The portions of fibrils either break off entirely or peel part way from the periphery of the fiber much like a banana is peeled. The brillation reduces the size and strength of the fiber, it also makes the liber appear fuzzy or frayed. Fabrics containing libers that librillate readily and which are dyed appear to change to lighter shades in those areas containing such liber because of the light-scattering effect of the librillated fibers. This is particularly noticeable in fabrics of the dark colors.

The amount of fibrillation of the liber may be determined and measured by the filtering properties or water tiow number of a certain weight of the liber that has been beaten in a Waring type mixer or beater for a certain period of time. The water flow number as used in this specilication and in the claims hereof is determined by adding 4 grams of the liber in 300 grams of water to a Waring type beater where it is beaten for 20 minutes. The liber in the water is screened by passing the slurry through an 80I mesh screen which removes the librils or particles that are broken olf. The screened liber and 18() grams of water are placed in a vBattista HF thimble having a sintered glass lilter plate therein. This thimble lilter is a standard article of commerce made by the Ace Glass Company of Vineland, NJ. and is described in a technical article entitled Hydro Cellulose Water Flow Number by O. A. Battista, l. A. Howsmon and Sidney Coppick in Industrial and Engineering Chemistry, volume 45, page 2107, September 1953.

The sintered glass lilter has an average pore size of 40 microns and is approximately one and one-quarter inches in diameter and one-sixteenth inch in thickness. The fiber When placed in the thimble with the Water is allowed to settle and form a liber pad on the lilter disc. The pressure on the lower side of the lilter disc is reduced by an amount equal toa pressure of 60 millimeters of mercury. The liquid is allowed to iiow through the librous pad and the sintered glass lilter while this slight vacuum is maintained. The time required for 100 cubic centimeters of water to liow through the liber pad and the sintered glass lilter plate is measured in seconds. This number of seconds is the Water flow number. The fibers of this invention that are relatively non-tibrillatable have a water flow number of less than 25.

Another important characteristics of staple libers is the card load factor. The card load factor is a measure of the amount of liber that is collected on or that loads a card cylinder during the normal textile carding operation and that is in effect lost to the textile operation. The card load factor may be so excessively high, that the carding machine after a period of operation becomes jammed and inoperative due to retention of the libers thereby requiring a shutting down and cleaning of the card. Conventional viscose rayon staple fibers have a card load factor which may vary from about 1.40 to about 4.00 and operate entirely satisfactory on the conventional carding machines.

The card load factor as used herein is determined by feeding 1.5 dener 1.5625 inch length regenerated cellulose staple liber to a standard Whitcn 40 inch revolving flat top card clothed with lilet Wire. The wire count is 100s on the cylinder and 110s on the dolfer and ats. The staple liber is fed toI the freshly stripped clean card cylinder by a spiked apron hopper feeder at the rate of 5 pounds per 20 minutes. The card is operated for 20 minutes and the liber that is collected or loads on the card cylinder is stripped by means of a stripping brush. The weight of the stripped liber from the card cylinder multiplied by 100 and divided by the weight of the liber fed to the card, namely, 5 pounds is the card load factor. With liner deniers and also with longer libers the card load factor is proportionally higher than the card load factor of 1.5 denier 1.5625 inches regenerated cellulose staple fibers.

In general, the staple liber of this invention has a card load factor not exceeding about 3.25 and is produced by spinning a certain viscose containing an amino viscose additive or spinning assistant into a low acid, low salt type sulfuric acid spinning bath that also contains zinc sulfate. The amino additive that is used is such that it chemically reacts with sulfur and zinc in the spinning processes and forms a zinc sulfur complex or compound, namely, a zinc dithiocarbamate compound that is insoluble in neutral and alkaline solutions. The zinc dithiocarbamate compound seriously and adversely affects the card load factor and, accordingly, the present invention provides an acid wash of the liber prior to drying to dissolve and remove this compound. The additives that may be used in practicing this invention include, for example, monoamines, such as dimethyl amine and diethyl amine, diamines such as ethylene diamine and other polyamines such as diethylene triamine. The amino additives may be used in a relatively small amount, for example, 1 to 4% based on the weight of the cellulose, either alone or in combination with other viscose additives such as dendro phenol, Carbowax and the like.

ln the production of high strength types of viscose rayon such as that utilized in tire fabric, it is common to add to the viscose ethoxylated aliphatic amines such as, for example, the ethoxylated amines derived from various animal and vegetable oils and fats. Examples of these types of additives are the commercial products set forth in U.S. Pats. Nos. 3,046,085 and 3,083,075. These types of additives when present in Viscose spun into zinc containing spinning baths may form zinc xanthates because of the terminal hydroxyl groups on the ethoxylated fatty or other aliphatic amines. The zinc xanthates are soluble and are readily removed during the subsequent after treatments to which the filaments and libers are subjected.

On the other hand, the amino additives employed in the present invention has at least one reactive amino hydrogen atom and accordingly in the presence of the zinc, there is formed an insoluble zinc dithiocarbamate compound which cannot be dissolved and removed by the usual subsequent after treatments. Thus, libers produced as described hereinafter Without an acid treatment in a relaxed condition after cutting to staple lengths and before drying exhibit card load factors which generally exceed 10% and may be as high as 55%. Such characteristic renders the libers unsatisfactory for use on these carding machines.

The viscose used in this invention comprises generally 4 to 9% cellulose, 5 to 10% caustic soda and from 30 to 38% carbon disulfide based on the weight of the cellulose. The sodium chloride salt point of the viscose may be from 7 to l2 and for some purposes vicose having a higher salt point of from 2 to 17 may be used. The viscose is spun into a low acid low salt type spinning bath containing from 5 to 10% sulfuric acid, 9 to 20% sodium sulfate and up to 9% preferably from 2.5 to 7% zinc sulfate with the spinning bath having a temperature of from 10 to 40 C. The liber that is formed is withdrawn from the spinning bath and is stretched from to 160% preferably 125 to 160% while being drawn through a hot dilute cascade acid bath containing of the order of 3% sulfuric acid, 5% sodium sulfate and 1.5% zinc sulfate at a temperature of to 100 C. The spinning speed is from 20 to 40 meters per minute. The freshly spun stretched fibers are cut into staple liber length and before drying, preferably immediately after cutting, are treated with a dilute acid at a concentration, temperature, and for a time suflicient to dissolve any reaction product or complex of the amino viscose additive and the sulfur and zinc present in the spinning operation; namely, the zinc dithiocarbamate compound. The acid may be sulfuric acid, hydrochloric or any other inorganic or organic acid that is compatible with the process and the equipment that is used, for example, a dilute solution of from 0.2 to 1.4% by weight sulfuric acid at a temperature of 96 C. and a treatment time of 15 minutes is suitable. The acid solution and the dissolved material is drained from the fiber and the liber is Washed and subjected to the other liquid treatments such as bleaching and di-sulphurizing and is then dried in the conventional manner.

The method of producing the regenerated cellulose fiber of this invention may be carried out with conventional equipment such as shown diagrammatically in the accompanying drawings wherein reference character 2 indicates generally a low acid low salt type spinning bath in which a spinneret 3 is positioned and to which the vicose is delivered by the rounder 4. The fiber 5 that is formed in the bath is directed to a stretching means comprising a pair of positively driven rollers or godets 6 and 7. The godet 7 is driven at a speed higher than the speed of godet 6 so that the fiber is stretched the desired amount while passing between them. The fiber is subjected to a high temperature dilute acid cascade bath in the trough 8 while passing between the godets which completes or substantially completes the regeneration of the cellulose. The fiber then passes in the form of a bundle or tow over the tow roller 9 to the cutting means 10' wherein the fibers are cut into short lengths as indicated by reference character 11. The cut fibers are delivered to a trough or zone 12 in which the fibers are treated with a dilute acid delivered by the spray 13 of such concentration and temperature, and for such time that the alkaliand waterinsoluble zinc sulfur amino compound or complex that is present is dissolved and is drained away through the discharge pipe 14. The stable fiber is then washed, bleached, desulfurized and dried in the conventional manner by conventional means which are not shown in the drawing.

The following examples are illustrative of the invention.

EXAMPLE I Viscose was prepared by treatment of pulp sheets (high alpha cellulose, viscose grade pulp) with caustic soda, shredding the resulting alkali cellulose, xanthating the alkali cellulose and dissolving it in a caustic soda solution. The viscose so prepared contains 6% cellulose, 7% caustic soda and 34% carbon disulfide based upon the weight of the cellulose. In this specific example, the cellulose to caustic soda ratio was 1.0 to 1.17. The viscose was then aged in the conventional manner at 18 C. for 12 hours. The viscose at the time of spinning had a sodium chloride salt test of 8.0, a ball fall viscosity of 60 to 75 seconds. The total sulfur content was 1.6% to 1.7% and the xanthate sulfur was 1.1% to 1.2%. 3.3% dimethylamine and 1.7% of a polyoxyethylene glycol ether of phenol containing an average of 15 ethylene oxide units per mole of phenol was incorporated in the viscose during the mixing operation. The dimethylamine and phenol ether may be added at any stage in the preparation of the viscose.

The viscose was spun to form a 1.5 denier, 12,000 filament yarn by extrusion of the viscose through orifices about 0.0025 inch in diameter into a spinning bath containing 7% sulfuric acid, 11% sodium sulfate and 4% zinc sulfate, the spinning bath being maintained at a temperature of about 30 C. The filaments were withdrawn from the bath, passed over a first godet, through a hot second bath, over a second godet and then collected and after treated. The second bath was formed by diluting some of the spinning bath and contained about 3% sulfurie acid, about 1.5% zinc sulfate and about 5% sodium sulfate and was maintained at a temperature of about 95 C. During passage of the filaments through the hot bath, they were stretched approximately The spinning speed was about 25 meters per minute. The fibers were cut to a staple fiber length of 1.5625 inches and before drying were subjected to a dilute solution of 1% sulfurie acid at 96 C. for 15 minutes to remove the zinc dimethyl dithiocarbamate formed by the reaction of the dimethyl amine viscose additive and the sulfur and the zinc present in the process. The dilute acid containing the dissolved material was drained away and the removal of the remaining compound or complex was completed during the subsequent liquid treatments before the fiber is dried. The fiber was then washed, desulphurized, bleached and dried in the conventional manner.

The physical properties of the filaments are set forth in the following table:

The Wet Stiffness Factor is the wet strength in grams per denier divided by the percent elongation in a wet state.

The Single Fiber Flex is measured on a Fiber Flex Tester made by Fiber Test Inc., Arcweld Building, Grove City, Pa. This testing machine measures the resistance of single fibers to fatigue in lexure. In this apparatus, a fiber is secured to a reciprocating element and passes over a carefully machined bar having an edge closely ground to a diameter of approximately 0.005 inch and the other end of the filament is secured to a small weight. As the element is reciprocated, the filament is drawn across the edge of the bar. The number of cycles up to the time the filament breaks is recorded. As reported in the above table, 10 filaments were subjected to this test and the number of cycles is reported at the time the sixth of the ten fibers fail. This is considered the median value. The corresponding Single Fibre Flex Test for cotton showed 69,000 cycles. This test is directly related to the wear properties of fabrics formed of the specific fibers. This method of testing fibers is described in an article by Lefferdink and Briar Interpretation of Fiber Properties published in Textile Research Journal, volume 29, June 1959.

The fibrillation is measured by subjecting the fibers to the action of a Waring type beater for 20 minutes and examining fibers under the microscope.

Additional examples of the spinning conditions and the properties of the resulting fiber are set forth on the attached Table II.

TABLE II S in bath Viscose, P p Fiber properties percent ereent Percent Percent Temp. Percent Tensile Elon ation Modulus Wet cs2 .S04 znso. .sor of stretch Denier Wet, g./d. g wet w stift 31 6. 8 5. 0 10. 0 33 156 1. 24 3. 39 17. 3 13.8 19. 6 34 7. 2 4. 7 10. 0 32 164 1. 28 3. 43 14. 4 14. 3 23. 8 37 9. 0 7. 5 10. 3 32 156 0. 82 3. 04 14. 0 13.9 21. 6 34 7. 2 3. 0 10.0 33 136 1. 21 3. 12 13. 1 15.2 23. 7 34 7. 1 8. 8 l0. 0 33 136 1. 14 3. 22 13.7 14.9 23. 5 34 6. 4 4. 9 11.6 30 149 l. 56 3. 12 24. 2 11. 7 12. 9 34 7. 0 3. 3 12. 0 30 149 1. 38 3. 73 16. 9 15. 2 20. 0 34 8.0 6. 8 12. 0 30 149 l. 46 3. 49 17.6 14. 1 18. 6 34 7. 3 5. 0 11. 6 80 140 1. 39 3. 56 19. 0 13. 5 18. 7

Further examples of the physical characteristics of ibers in accordance with this invention are shown in Table III.

TABLE IIL-SINGLE FIBERS Other examples of methods of forming the bers of this invention are shown in the following Table IV.

TABLE IV Spin hath Spinning viscose, Temp., Percent Percent Percent Stretch Salt test C. H2504 ZnSO4 Na2SO4 percent While preferred embodiments of this invention have been shown and described, it is to be understood that changes and variations may be made without departing from the spirit and scope of this invention as dened in the appended claims.

We claim:

1. A method of forming regenerated cellulose fibers which comprises extruding into a spinning bath comprising 5% to 10% sulfuric acid, 9 to 20% sodium sulfate and zinc sulfate in an amount up to 9%, a viscose spinning solution containing an amino viscose additive that forms with sulfur and zinc a zinc dithiocarbamate compound that is insoluble in water and alkaline solutions to form continuous laments containing a zinc dithiocarbamate compound, cutting the filaments into staple ber lengths, treating the staple length bers in a completely relaxed state with a dilute acid solution having an acid concentration and a temperature and for a time sucient to dissolve and remove from the bers the zinc dithiocarbamate compound that was formed, the treatment with the dilute acid solution being equivalent to treatment of the fibers with an aqueous solution containing from 0.2% to 1.4% by Weight of sulfuric acid at a temperature of 96 C. for 15 minutes and subjecting the staple length fibers to aqueous treating liquids and drying.

2. The method of forming regenerated cellulose bers as dened in claim 1 wherein the amino viscose additive is a monoamino viscose additive.

3. The method of forming regenerated cellulose bers as defined in claim 1 wherein the amino viscose additive is a monoamino viscose additive and the staple length bers are treated with an aqueous solution containing from 0.2% to 1.4% by weight of sulfuric acid at a temperature of 96 C. for 15 minutes.

4. The method of forming regenerated cellulose tibers as defined in claim 1 wherein the amino viscose additive is dimethyl amine and the staple length fibers are treated with an aqueous solution containing from 0.2% to 1.4% by weight of sulfuric acid at a temperature of 96 C. for 15 minutes.

References Cited UNITED STATES PATENTS 2,297,746 10/ 1942 Charch et al. 264-168 2,515,834 7/1950 Nicoll 264-168 2,696,423 12/ 1954 Dietrich 264-197 X 3,046,085 7/1962 Burrough et al. 264-197 X 3,083,075 3/1963 Saxton 264-197 3,277,226 10/1966 Bockno et al. 264-188 2,852,333 9/1958 Cox et al. 264-168 FOREIGN PATENTS 37,161 1/1962. Japan. 6,401,760 8/ 1969 Netherlands.

JULIUS FROME, Primary Examiner J. H. WOO, Assistant Examiner U.S. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTIGN Patent No. 3,529,052 Dated September 15, 1970 Inventods) Rufus T. Carney and Charles J. Geyer, Jr.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as show-n below:

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